okay I'm a little lost on this one :/

which choice correctly completes the sentence?
-Gently, they ______ the tiny eggs back in the nest.
*set
had setted
sat
had sat(this one looks like it could work too)

how do I know if the sentence is in present or past tense?

Your answer is right.

To determine the tense of a sentence, you need to examine the verb used. In this case, the verb is "set" or "sat." Both "set" and "sat" can be used in both present and past tense, depending on the context.

In the sentence you provided: "Gently, they ______ the tiny eggs back in the nest." The context suggests that the action of putting the eggs back in the nest has already happened in the past. Therefore, the sentence should be in the past tense.

Now let's look at the options:

1. Set: This is the simple past tense of the verb "set." Since the sentence is in the past tense, "set" is a suitable option.

2. Had setted: "Setted" is not a correct form of the verb "set" in standard English grammar. The past tense of "set" is simply "set."

3. Sat: "Sat" is the past tense of the verb "sit." However, it doesn't fit the context of the sentence. In this scenario, the action is about putting the eggs back in the nest, not sitting on them. So "sat" is incorrect in this context.

Based on the analysis, the correct choice is "set."